Pearls are among the most esteemed gemstones and have been highly valued throughout recorded history. The relative scarcity of naturally forming pearls has lead many people to experiment with various methods for producing cultured pearls. The Chinese appear to have developed the first commercially successful cultured pearl production method, perhaps beginning in as early as the fifth century. They inserted various objects between the shell and mantle tissue of freshwater pearl mussels, returned them to the water, and recovered the mussels a year or more later to find the inserted objects coated with mother-of-pearl, which is also referred to as nacre. Similar methods are still being used today to produce what are alternatively known as Mabe, Chicot, or half pearls using various types of mollusks such as freshwater mussels, saltwater oysters, and abalone.
In the mid-1700s, a Swedish naturalist, Carl Linne, induced the formation of free pearls in European freshwater pearl mussels by inserting objects through holes in the mussels' shells and holding the objects away from the shells using fine silver wire. The first commercially successful process for culturing free pearls was developed in Japan by Kokichi Mikimoto (using methods variously attributed to Otokichi Kuwabara, Tokichi Nishikawa and Tatsuhei Mise) beginning in the late 1800s. Mikimoto's technique involves making an incision in the organs of a pearl oyster, placing a nucleus within this incision, and placing a piece of mantle tissue against the nucleus that forms a sac that eventually covers the entire nucleus with nacre. This method is used to produce the majority of Japanese cultured pearls (sometimes referred to as Akoya pearls) as well as “South Sea” pearls that are being produced in Tahiti, Australia, and several other countries in the South Pacific. In terms of overall economic value, the Mikimoto method is used today to produce pearls that represent the largest part of the worldwide pearl market.
An alternative non-nucleated pearl culturing method has also been developed that involves inserting several pieces of mantle tissue into incisions in the mantle organ of a freshwater mussel. This method is primarily being used in China. In terms of total weight of pearls produced, this type of method accounts for a large fraction of worldwide pearl production, although in economic terms it remains a distant second to pearls produced by the Mikimoto method discussed above.
Significant problems or limitations exist with each of these methods of pearl production. Only approximately one half of the outer surface of Mabe pearls are covered by nacre, making them suitable for only certain types of jewelry, such as earrings or pendants. Mabe pearls represent a very small fraction of the pearl jewelry market.
Current nucleated pearl production methods are quite difficult and laborious, technically and practically. Learning where and how to appropriately make the incision into the oyster's organs, insert the nucleus, and insert the piece of mantle tissue next to the nucleus requires substantial training. It has been estimated that it often takes several hundred supervised attempts at seeding pearl oysters before a trainee begins to be competent at the pearl seeding process. This process is also quite traumatic on the pearl oyster and even when a skilled technician is used, “vomits” (where the pearl oyster “spits out” the nucleus soon after insertion) and “deaths” (where the pearl oyster dies soon after insertion) can often exceed 50% of the implanted oysters. Because the nucleus insertion process is very delicate and difficult, there is a worldwide shortage of skilled oyster nucleating technicians and these technicians are often able to demand to be paid a high fraction of the pearls that are eventually produced as a result of their seeding efforts.
Even if the pearl oyster survives the insertion process and retains the nucleus, the quality of the pearl produced will not be known until the pearl oyster is harvested and opened, typically between a year and a half and three years after the nucleus has been inserted. Only a relatively small percentage of the pearls produced will be of the highest quality. The portion of the harvest that is round or semi-round, with fine to good luster, and nacre surface with few or no blemishes will be designated as “A” or “B” grade. These pearls usually comprise between only 2% and 10% of a crop, but may represent between 30% and 50% of the overall value of the harvest. It is common, for instance, for some pearls to be irregularly shaped (a large number of Tahitian pearls, for instance, have a distinctive shape called “circles” where the pearls are surrounded by dark latitudinal striations), suffer from significant surface imperfections, etc. The size and shape of the pearl that will be eventually be produced will depend on the type of mollusk used, the size and shape of the nucleus (nuclei are typically almost perfectly spherical), the size, shape and placement of the incision made by the technician, the positioning of the piece of mantle tissue inserted with the nucleus, and the growth time and final nacre thickness. While they are sometimes produced accidentally, the Mikimoto method is not conducive to intentionally producing fancy shaped pearls, such as teardrop or pear shaped pearls.
While some failures in the nucleation process may be detected within the first several days or few weeks (because the oyster dies or the nucleus is rejected), the success of the majority of the other nucleation attempts will not be known until the oyster is eventually harvested. Only after the oyster has been cared for during the typically one and a half to three year nucleation period will it be known whether the implantation process was successful or not. Thus while the relatively few pearls produced by this method that are perfect or nearly perfect are often extremely beautiful and valuable, the method currently being used to produce nucleated cultured pearls leaves a great deal to be desired.
Pearls produced using the non-nucleated method discussed above are typically irregularly shaped and are almost always far less attractive (in terms of size, shape, color, and nacre quality) and far less valuable than nucleated pearls.
For these reasons, it would be of great benefit to be able to produce nucleated cultured pearls using a method that do not suffer from one or more of the problems described above or that offers one or more of the benefits described below.